Lens for a signal lamp

ABSTRACT

A lens for a signal lamp, such as an emergency or warning lamp, that is intended to surround the source of light, which source is preferably elongated. The lens has a wall that is curved about the center of the light, with an outer surface relatively smooth and an inner surface which is also relatively smooth, but is provided with a plurality of lenticular light spreaders spaced along the surface thereof at appropriate intervals such that a substantial portion of all of the light passing through the surface of the lens that is visible to the viewer will be directed from the source, either through the plane surface of the lens or through the lenticular light spreaders substantially to a common point. Thus, a viewer will have a substantial portion of all of the light rays emanating from the light source through the visible surface of the lens, directed to his eye throughout the entire width of the lens.

United States Patent 1 Bailey et al.

n11 3,826,914 [4 July 30, 1974 LENS FOR A SIGNAL LAMP [76] inventors: John J. Bailey; William C. Keeran,

both of 1701 N. Ashland Ave., Chicago, 11]. 160622 [22] Filed: Nov. 21, 1972 [21] Appl. No.: 308,436

Primary Examiner-Samuel S. Matthews Assistant Examiner -Russell E. Adams, Jr.

Attorney, Agent, or Firm-Burns, Doane, Swecker &

Mathis out the entire width of the lens.

[57] ABSTRACT A lens for a signal lamp, such as an emergency or warning lamp, that is intended to surround the source of light, which source is preferably elongated. The lens has a wall that is curved about the center of the light, with an outer surface relatively smooth and an inner surface which is also relatively smooth, but is provided with a plurality of lenticular light spreaders spaced along the surface thereof at appropriate intervals such that a substantial portion of all of the light passing through the surface of the lens that is visible to the viewer will be directed from the source, either through the plane surface of the lens or through the lenticular light spreaders substantially to a common point. Thus, a viewer will have a substantial portion of all of the light rays emanating from the light source through the visible surface of the lens, directed to his eye through- 10 Claims, 10 Drawing Figures PAIENIEU Mama I sum 1 0r 2 1 LENS FOR A SIGNAL LAMP BACKGROUND OF DISCLOSURE light emitted therefrom toward the viewer and whereby the greatest light intensity will be developed throughout the entire lens. The latter, in many instances, forms a dome over the source of light. I

In having a warning lamp with a source of light provided by a tungsten filament or xenon tube, it is visible in all directions, but with the type of lenses available heretofore, it lacks both intensity and size. Many attempts have been made heretofore to concentrate the light and to direct it to certain desired areas, but these have not been entirely satisfactory.

A lens that has a tungsten filament with a plain glass cylinder around it uses the cylinder only to protect the source of light. It is immediately recognized that the only visible light in such case is that which is seen directly from the lamp filament. All other light rays are lost in space and are neither concentrated nor directed toward the viewer.

An attempt to modify the light rays involved the use of a fresnel lens surrounding the source of light. This involved a lens portion with external narrow planes or grooves above and below the center of the light source, but the inner surface of the surrounding lens was smooth. Thus, there was no means provided for optically directing to the viewer any of the rays of light passing through the glass other than the direct rays emanating from the light source in any vertical plane from the light source toward the viewer.

Another form of lens used heretofore provided vertical flutes on the inner wall of the cylinder that surrounded the light source. These vertical flutes were formed as sectors of circles in direct sequence throughout the inner surface of the cylinder. These flutes would direct a somewhat wider panel of light toward the viewer, but unless some external means were provided on the cylinder, the viewer would see only a panel of light approximately the height of the filament and the width of the cylinder.

In summary, when the cylinder that surrounds the source of light has neither the fresnel lens on the outside nor the flutes on the inside, the visible light to the eye of a person observing the lamp would be substantially the size of the filament configuration. When the cylinder has the external fresnel lens, but no internal flutes or light spreaders, the light visible to the eye of a person observing the lamp is a panel the width of the filament and the height of the cylinder. When the cylinder that surrounds the source of light has internal light spreaders or flutes, but has no external lens nor fresnel lens, the light that is visible to the eye of a person observing the lamp is a panel of light the height of the filament andthe width of the cylinder.

light approximates the height and width of the cylinder as it is observed by the eye of the viewer.

The use of external lenses or fresnel lenses or any grooving or fluting of the external surfaces of lamps causes a considerable reduction in the'intensity of the light emission therefrom. This is due in part at least to the accumulation in the grooves andon the surfaces thereof of dirt and other foreign matter which would reduce the light emission to a dull glow making it impossible to utilize the sparkling brilliant capability of the xenon as a source of light. This reduction is also caused by the greatly increased thickness of the dome or cylindrical wall which is required for the grooving of the external surface thereof.

The use of internal contiguous or closely adjacent vertical light spreaders or flutes also causes a considerable reduction in the intensity of the light emission therefrom. Those light spreaders that are in adirect line between the light source and the eye of the viewer will greatly reduce the visible intensity of the normally visible direct rays from the light source by redirecting some of those normally visible direct rays so that a portion of them will be redirected sufficiently to be out of the range of the eye of the viewer..

One object of this invention is to obviate the objections encountered with lenses used'heretofore .especially for'signal or warning lamps and to improve the construction thereof to provide intensive brightness and a large area of visibility. 7

Another object of the invention, since the attentiongetting capability of a lamp is in proportion to its size, is to obtain a large area of light emanating from a light source and directed to a common point, such as the eye of a viewer, but without the disadvantages of an external lens or fresnel lens and with a minimal reduction of the brightness of both direct rays and redirected rays from the light source to the eye of the viewer.

These objects may be accomplished according to certain embodiments of the invention by providing a lens surrounding a light source, preferably an elongated light source, which has relatively smooth outside and inside surfaces so as to allow direct rays from the light source to pass through the lens to the eye of the viewer. The inside surface, however, has spaced lenticular light spreaders at intervals along the area thereof and extending in substantially circular relation throughout the height of the lens. The spacing and shape of the lenticular light spreaders relative to the curvature of the wall of the lens is such as to optically direct normally unseen light rays from the light source to the eye of the viewer as well as direct rays and thereby obtain a large area of light of brilliant intensity.

BRIEF DESCRIPTION OF THE DRAWINGS These embodiments of the invention are illustrated in the accompanying drawings, in which:

FIG. 1 is a side elevation of a signal lamp using a lens or dome that embodies this invention;

FIG. 2 is a cross section through the lens or dome showing one form of light source therein;

FIG. 3 is a similar view showing another form of light source;

FIG. 4 isa similar view showing still another form of light source;

F IG. 5 is a similar view showing still another form of light source;

FIG. 6 is a cross section through the lens or dome, with a lining therein;

FIG. 7 is a side elevation of the lens or dome illustrating the lenticular light spreaders;

FIG-8 is a cross section therethrough on the line 8-8 in'FIG. 7;

FIG. 9 is a diagrammatic view showing the light rays; and

FIG. 10 is an enlargement of the cross section of one light spreader showing the refraction of a ray of light.

DETAILED DESCRIPTION OF DISCLOSURE The invention is illustrated in connection with a flashing or warning signal lamp such as may be applied to emergency vehicles, and in any other environments where it is desirable to obtain a maximum area of light, through both direct rays and redirected indirect rays, and a minimum reduction of the brightness.

One example of this type of lamp, to which this invention may be applied, is disclosed in Bailey Pat. No. 3,504,339, granted Mar. 31, 1970. This type of lamp is illustrated generally in FIG. 1, with a base 1, upon whicha lens or dome 2 is seated and secured. The base 1 encloses the light generating and flashing means, such, for example, as batteries, transformers, etc. The operation thereof is described more fully in the aforesaid Pat. No. 3,504,339.

The dome 2 includes a surrounding wall 3 which is shown as frustoconical although other shapes may be used as desired. The wall 3 has a closed top 4 thereof formed in one integral piece with the wall. A depending skirt 5 is formed at the lower edge of the surrounding wall to be seatedupon the upper end of the base 1. Any suitable means (not shown) may be used for securing the dome 2 upon the base 1, such as screw fastenings, adhesive, etc.

The dome 2 is preferably formed of transparent material. In accordance with custom for emergency vehicles or signal lamps in other environments, light coloring may be used in this material, as amber, light red, light blue-,'etc., without substantial obstruction of the visibility of the light rays therethrough. A suitable plastic material may be used for this purpose.

A source of light is provided in the center of the dome 2. This light source may be a space discharge tube, such as a xenon tube, and may be in different shapes as illustrated in FIGS. 2 to 4, but preferably should illuminate substantially the entire height of the dome 2. The light may be an incandescent tungsten filament, such as a sealed beam lamp 6' in the rotating type of vehicle warning lamp as illustrated in FIG. 5.

In FIG. 2, the xenon tube 6 is located midway of the height of the dome 2, at the focal axis of parabolic reflectors 7, described more fully in the aforesaid Bailey Patent, No. 3,504,339. This will cause a distribution of light substantially throughout the height of the dome. This design of light source functions particularly well in this invention because it hasappreciably greater width than is usually found in a light source for this purpose. Also the greater width of the sealed beam light source shown in FIG. 5 is advantageous with this invention.

Instead of using a ring-type xenon tube, the source of light may be a long vertical inverted U-shaped xenon tube as indicated at 8 in FIG. 3, or a long helical xenon 4 tube as indicated at 9 in FIG. 4. Each of the latter extends substantially throughout the height of the wall. of dome 2 at the center thereof. Any xenon configuration that is approximately equal to the inside vertical height of the dome would be suitable for use. The electrodes for the space discharge tube are not illustrated.

Instead of using a xenon tube, a sealed beam lamp may be used as in the well-known rotating type of vehicle warning lamp, may bethe source of light as indicated at 11 in FIG. 5. This type of light source extends substantially throughout the inside vertical height of the dome and has the additional advantage of being a wide source.

In cooperation with the central'light source along the height of the surrounding wall, there is provided lenticular light spreaders spaced at intervals around the cir-.

cumference thereof. These are not shown in FIGS. 2 to 5 for simplicity of illustration, but are shown in FIGS. 6 to 10. These light spreaders may be provided either on the inner surface of the wall 3, which is otherwise substantially smooth, or on a transparent plastic liner 10 which is separately inserted inside the dome 2. The outside surface of the dome 2 isalso smooth.

The lenticular light spreaders are illustrated at 12 in FIGS. 6 to 10, and are spaced apart a distance determined by an equation that will be explained later. The spacing will be apparent from FIGS. 7 and 9. They are preferably of uniform width. As an example, in a dome 2 that has a base diameter of 8 inches, there may be 30 lenticular light spreaders throughout 360 of the conical wall, each approximately three-eighths inch in width and spaced an equal distance aparLTheyextend in substantially parallel relation throughout the axial length of the wall 3, on the smooth inner surface thereof.

These light spreaders will have a controlled flow of light that in effect makes the entire inside surface of the dome appear lighted. Since the light spreaders are a relatively thin average addition to the wall thickness of the dome, the reduction of light transmission due to the increased wall thickness is slight. When the dome is of tinted plastic, the color of the plastic may have to be adjusted slightlyto compensate for the increase-in wall thickness at the light spreaders. However no adjustment need be made if a clear plastic liner with integral light spreaders is separately inserted inside the dome between the dome wall and the light source as shown in FIG. 6.

Since the light source is nearly equal in'size to the dome height and is appreciably smaller than the dome diameter, light spreaders are used to redirect the light rays that, without light spreaders, would be passing at angles through the dome and be unseen by the viewer. Any light spreaders in a direct line between the light source and the viewer will slightly diminish the intensity of those rays. Therefore for most efficient light transmission it would be desirable to have no light spreaders in that portion of the dome through which rays could pass in a direct line from the light source to the viewer and have light spreaders only on either side of these direct rays to bring those that would be normally unseen back into the sight of the viewer.

In FIG. 9 the inner circumference of the dome (or liner) is divided into arcs of preferably equal lengths and light spreaders are located at the ends of the arcs leaving a space between each pair of light spreaders. As the viewer looks at the center of the front of the dome,

. the light spreaders are relatively far apart. As his line of vision is turned to either side of the center, the horizontal distance between each adjacent pair of light spreaders becomes less and less until at the extreme sides the light spreaders appear to be contiguous. Thus at the center of the front where the light spreaders are not desirable, they are spaced farthest apart and toward the sides they are closer together, a condition that is desirable. This effect is shown by the dimensions A through F where F is the'largest, E is smaller thanF, D is smaller than E, C is smaller than D, B is smaller than C and A is the smallest. Thus the light spreaders are closer together in those areas where their effect is most needed to redirect rays toward the viewer and farther apart where they may possibly be interfering with the maximum transmission of light. The result is that the whole dome is lighted with high overall efficiency.

Any time a lens or spreader is inserted in the way of a ray of light that normally would beam directly from the light source to the viewer, the lens or spreader will interfere with the ray and affect its intensity. Thus where direct rays are involved, we should have the rays pass through only the plain dome without any lens or spreader. On the other hand, all other rays except direct rays passing through the dome will be invisible (unseen) unless some means such as a lens or spreader is incorporated into the dome (or liner) to divert them and redirect some 'of them to the viewer. To achieve that, we have a lens or spreader on all of the surface of the dome except that their spacing apart is greatest on that portion of the surface through which the normally direct rays to the viewer will pass.

By using a talllight, we have provided a means to have direct rays visible to the viewer for approximately the full height of the dome. Therefore, by improving the collection and redirecting of the indirect (unseen) rays the result is a vast improvement in the effectiveness of the dome. We have done this by a spacing of the light spreaders. In other words, we have placed the light spreader flutes in an arrangement whereby there will be fewer of them in a position to interfere with direct rays but still sufficient numbers of them beyond that area to redirect a large number of the indirect rays that otherwise would be unseen. Since the light spreader flutes appear to light up as they redirect the indirect light rays, the whole dome appears to be lighted in a series of vertical narrow panels that are closer and closer together as the viewers vision moves toward the left or right hand edges of the dome so that the panels of light at the edges are practically joined together.

The dome has means to obtain a large area of light substantially throughout the entire inner surface of the dome from a light source at the center thereof. This is accomplished without the use of external fresnel lenses that are difficult to clean or to keep clean. The resulting area of light since it is considerably larger than the light source itself greatly improves the capability of the signal lamp to attract attention because light intensity is not as important as visibility which is a factor of intensity per unit area times total area.

The relationship between the width of each light spreader and the space between adjacent spreaders can be defined by a simple equation. Where w =width of light spreader, s =width of space, n number of light spreaders in the dome circumference and d average inside diameter of a frusto-conical dome,

' the values of n and w must be determined experimentally for each width and shape of light source. Such tests have developed a pattern of the range for-the width of the space between the spreaders that can be expressed by the ratio of s to w for various values of n. From the above equation:

The following table is an analysis of the above ratio for several values of n and for two values of w, namely 0.375 inch and 0.3125 inch, when incorporated in a dome having an average diameter of 7 inches.

n s/0.375 80.3 I 2 When used with a light source of the type described in Bailey Pat. No. 3,504,339, the performance .of the signal lamp peaked at 25 spreaders having a width of 0.375 inch and at 30 spreaders of 0.312 inch width, or when the ratio for s to w is about 4 to3. When using various narrower light sources, the performance peaks at as low as 2 to 5 and with wider light spreaders at about 5 to 2.

FIG. 10 is an enlarged view of one of the lenticular light spreader cross sections shown in FIG. 9. it shows how a light ray will be refracted and thus'redirected as it passes through a light spreader. Line AB is.a base line from which the angle of refraction is determined. The equation for computing the angle of refraction for the'plastic material used for the dome is:

It is this refraction of the rays that redirects some of the normally unseen rays until they are visible to the viewer and thereby increases the quantity and area of light visible to him.

While the invention has been illustrated and described in certain embodiments, it is recognized that other variations and changes may be made therein, without departing from the invention set forth in the claims.

We claim: I

- 1. A lens for a lamp having a light source, said lens comprising a wall curved at least through a semi-circle about a center substantially at the light source and with a relatively smooth outer surface and a relatively smooth inner surface, said inner surface having lenticular light spreaders thereon and spaced apart transversely of said inner surface, each of the light spreaders 7 having a convex surface facing toward the center of the semi-circular inner surface and spaced apart along said semi-circular inner suface with arcuate areas between the light spreaders having a center at the center of the semi-circle, the spacing of the lenticular light spreaders and the curvature of the inner surfaces thereof toward the light source being so proportioned relative to the arc of the curved wall that substantially all of the light rays in a semi-circle of the wall will be directed substantially toward a common point.

2. A lens according to claim 1, wherein the wall is of uniform thickness between the spaced light spreaders.

3. A lens according to claim 2, wherein the light source is elongated axially of the lens throughout substantially the length of the lenticular light spreaders.

4. A lens for a lamp having a light source, said lens comprising a wall curved at least through a semi-circle about a center substantially at the light source and with a relatively smooth outer surface and a relatively smooth inner surface, said inner surface having lenticular light spreaders thereon and spaced apart transversely of said inner surface, the spacing of the lenticular light spreaders and the curvature of the inner surfaces thereof toward the light source being so proportioned relative to the arc of the curved wall that substantially all the light rays in a semi-circle of the wall will be directed substantially toward a common point, the lenticular light spreaders being formed of one integral piece with the wall and having convex inner sur faces facing toward the center of curvature of the wall.

5. A lens according to claim 1, wherein the wall inner surface is cylindrical between the light spreaders and on an arc having a center coincident with the center of the curved wall.

6. A lens according to claim 5, wherein the light spreaders are substantially semi-circular in cross section and are spaced apart on the inner'surface of the wall no less than 30 percent of the width of the light spreader nor more than 5 times the width of the spreader.

7. A lamp comprising a base having an elongated light source extending upwardly therefrom, a dome mounted on the base and including a surrounding wall curved on a center substantially at the light source, said wall having substantially smooth outer surface and inner surface, said inner surface having lenticular light spreaders extending lengthwise thereof and spaced apart transversely, each of the light spreaders having a convex surface facing toward the center of the semicircular inner surface and spaced apart along said semicircular inner surface with arcuate areas between the light spreaders having a center at the center of the semi-circle, the spacing of the lenticular light spreaders and the curvature of the inner surfaces thereof toward the light source being so proportioned relative to the curvature of the surrounding wall that substantially all of the light rays in a semi-circle from the source of light will be directed by the lenticular light spreaders and by the substantially smooth surfaces therebetween toward a common point.

8. A lamp according to claim 7, wherein the lenticular light spreaders are formed of one integral piece with the wall.

9. A lamp according to claim 7 wherein the wall between the light spreaders is of uniform thickness.

10. A lamp according to claim 7, wherein the dome includes a top over the upper end of the wall, and the light source extends substantially throughout the height of the dome at the center thereof. 

1. A lens for a lamp having a light source, said lens comprising a wall curved at least through a semi-circle about a center substantially at the light source and with a relatively smooth outer surface and a relatively smooth inner surface, said inner surface having lenticular light spreaders thereon and spaced apart transversely of said inner surface, each of the light spreaders having a convex surface facing toward the center of the semi-circular inner surface and spaced apart along said semicircular inner suface with arcuate areas between the light spreaders having a center at the center of the semi-circle, the spacing of the lenticular light spreaders and the curvature of the inner surfaces thereof toward the light source being so proportioned relative to the arc of the curved wall that substantially all of the light rays in a semi-circle of the wall will be directed substantially toward a common point.
 2. A lens according to claim 1, wherein the wall is of uniform thickness between the spaced light spreaders.
 3. A lens according to claim 2, wherein the light source is elongated axially of the lens throughout substantially the length of the lenticular light spreaders.
 4. A lens for a lamp having a light source, said lens comprising a wall curved at least through a semi-circle about a center substantially at the light source and with a relatively smooth outer surface and a relatively smooth inner surface, said inner surface having lenticular light spreaders thereon and spaced apart transversely of said inner surface, the spacing of the lenticular light spreaders and the curvature of the inner surfaces thereof toward the light source being so proportioned relative to the arc of the curved wall that substantially all the light rays in a semi-circle of the wall will be directed substantially toward a common point, the lenticular light spreaders being formed of one integral piece with the wall and having convex inner surfaces facing toward the center of curvature of the wall.
 5. A lens according to claim 1, wherein the wall inner surface is cylindrical between the light spreaders and on an arc having a center coincident with the center of the curved wall.
 6. A lens according to claim 5, wherein the light spreaders are substantially semi-circular in cross section and are spaced apart on the inner surface of the wall no less than 30 percent of the width of the light spreader nor more than 5 times the width of the spreader.
 7. A lamp comprising a base having an elongated light source extending upwardly therefrom, a dome mounted on the base and including a Surrounding wall curved on a center substantially at the light source, said wall having substantially smooth outer surface and inner surface, said inner surface having lenticular light spreaders extending lengthwise thereof and spaced apart transversely, each of the light spreaders having a convex surface facing toward the center of the semi-circular inner surface and spaced apart along said semi-circular inner surface with arcuate areas between the light spreaders having a center at the center of the semi-circle, the spacing of the lenticular light spreaders and the curvature of the inner surfaces thereof toward the light source being so proportioned relative to the curvature of the surrounding wall that substantially all of the light rays in a semi-circle from the source of light will be directed by the lenticular light spreaders and by the substantially smooth surfaces therebetween toward a common point.
 8. A lamp according to claim 7, wherein the lenticular light spreaders are formed of one integral piece with the wall.
 9. A lamp according to claim 7 wherein the wall between the light spreaders is of uniform thickness.
 10. A lamp according to claim 7, wherein the dome includes a top over the upper end of the wall, and the light source extends substantially throughout the height of the dome at the center thereof. 